Background Gonorrhea may infect the urethra, rectum, and oropharynx in men. It may only be acquired when there is contact between infected and uninfected anatomical sites. Seven plausible routes of MSM transmission have been proposed: urethra-to-rectum, rectum-to-urethra, urethra-to-oropharynx, rectum-to-oropharynx, oropharynx-to-urethra, oropharynx-to-rectum, and oropharynx-to-oropharynx. We characterize the uncertainty and potential importance of transmission from each anatomical site using a deterministic compartmental mathematical model.

Methods We developed a model of site-specific gonococcal infection, where individuals are infected at zero, one, two, or all three sites. Sexual behavior and infection duration parameters were fixed similar to recent analyses. Markov Chain Monte Carlo methods were used to sample the posterior distribution of transmission probabilities that were consistent with site-specific prevalence in American MSM populations under specific scenarios. Scenarios were defined by whether transmission routes may or may not transmit by constraining specific transmission probabilities to zero rather than fitting them.

Results Transmission contributions from each site have greater uncertainty when more routes may transmit, when all routes may transmit, the oropharynx can contribute 0–100% of all transmissions. In contrast, when only anal or oral sex may transmit, transmission from the oropharynx can account for only 0–25% of transmission. Intervention effectiveness against transmission from each site also has greater uncertainty when more routes may transmit.

Conclusion Multiple routes of transmission leads to great uncertainty. Even under ideal conditions (i.e., when site-specific gonococcal prevalence, relative rates of specific sex acts, and duration of infection at each anatomical site are known and do not vary), the relative importance of different anatomical sites for gonococcal transmission cannot be inferred with precision. This result is generalizable to any other infection where multi-site infection leads to multiple routes of transmission. Additional data informing per act transmissibility are needed to understand site-specific gonococcal infection transmission. This understanding is essential for predicting population-specific intervention effectiveness.

Disclosure No significant relationships.